<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        
        function sum(abc){
            // return abc.split("").reverse().join("");
            var a=abc.split("");
            var b=a.reverse();
            var c=b.join("");
            return c;
        }
        var res=sum("12345");
        console.log(res)
    </script>
</body>
</html>